1. Field of the Invention
The invention relates to a solvent condenser for an apparatus for recovering solvent from a carrier gas/solvent mixture.
2. Description of the Prior Art
In many industrial processes, for example in the coating and drying of tapes, foils, etc., such as audio or video tapes, solvent vapours arise which must be collected and recovered because they are mostly explosive when mixed with air and are almost always harmful to health as well. As a rule, the driers, and frequently also the coaters, are encapsulated, shielded from the access of air and held under an inert atmosphere, for example nitrogen. At the same time, the locks are supplied with inert gas. This avoids the possibility of an explosion and prevents the escape of vapours which are a health hazard.
A modern solvent recovery apparatus, as disclosed for example in elder European patent application 90 116 885.6 therefore as a rule comprises two circuits independent of each other, that is
a carrier gas circuit from which the solvent is condensed out and PA0 a low-temperature section with which the locks of the manufacturing plant, for example a drier, are supplied.
From DE-A 35 01 643 a method is known for recovering solvents in cleaning processes employing organic solvents in which the solvent present in the form of a mixture of solvent vapour and air after pumping off the liquid solvent constituents is partially condensed out by cooling in a solvent condenser. The recovery of the solvent or solvents is by condensation in the vapour chamber of a solvent condenser by heat exchange with a refrigerant which vaporizes thereby. The refrigerant is conducted in a closed circuit via this solvent condenser or refrigerant evaporator, a compressor, a refrigerant liquefier and via an expansion valve.
In the solvent condenser excess solvent constituents are condensed and supplied to a solvent supply tank. The solvent vapour collecting in accordance with the saturation partial pressure in the vapour chamber of the solvent condenser passes thereafter into the refrigerant liquefier and is there heated against the refrigerant which is in turn liquefied.
A similar arrangement of refrigerant evaporator and condenser disclosed in GB-A 20 10 104. The refrigerant condenser and the refrigerant evaporator are each accommodated in gas-tight containers. A liquid mixture comprising a volatile component to be recovered is introduced into the container with the refrigerant condenser. The liquid mixture is heated by heat exchange with the condensing refrigerant, the volatile component vaporizes and the vapour is introduced into the other container containing the refrigerant evaporator, where the volatile component condenses again. The heat thereby extracted from said component is transferred to the refrigerant conducted in the circuit through the two containers.
Two alternately driven heat exchangers incorporated into an apparatus for recovering the hydrocarbons contained in a gasoline-air mixture are disclosed in DE-C 23 37 055. The gasoline-air mixture is thereby cooled in the regenerated of the two alternatable heat exchangers to such an extent that by freezing out the uncondensed hydrocarbons and the remaining water vapour are also separated from the air. Prior to its cooling, for regeneration of the other heat exchanger charged in an earlier operating phase the gasoline-air mixture is first supplied to said heat exchanger and then returned to the regenerated heat exchanger. A similar heat exchanger arrangement for a solvent recovery apparatus is also known from DE-A 39 30 239, which was not prior published.
If, as in these known continuously operated solvent condensers, a solvent condenser is used which on the refrigerant side is constructed as injection evaporator, i.e. in which the refrigerant completely vaporizes in the tubes of the evaporator and the fluid to be cooled is conducted round the tubes, then although the amount of circulating refrigerant can be kept small, there is the disadvantage that in this evaporator design the irregular distribution of the refrigerant has a disadvantageous effect on the tubes and in the latter, and as a result the surface temperature thereof is likewise irregular.
Apart from the injection evaporator, in the literature (cf. Lueger, Lexikon der Technik, of 1970, volume 16) the so-called flooded evaporator is known in which the evaporator container is almost filled with refrigerant and the medium to be cooled is conducted in a tube coil or a tube bank in the evaporator container through the liquid refrigerant. The refrigerant vapour is extracted at the upper part, usually via a vapour dome.
It is known from U.S. Pat. No. 4,276,751 that flooded evaporators connected in parallel can be used in an automatic ice machine for forming ice from water. In this case, the configuration as flooded refrigerant evaporator is an obvious choice simply because of the desired ice formation. For this purpose, the water necessary is flooded by refrigerant in the cells of a container and cooled until ice forms. During the entire cooling the water rests in the cells, which give the ice forming the desired shape. After conclusion of each ice-forming cycle "hot" refrigerant gas flows round the container with the ice in order to detach the latter from its cells. Because of the nature of the ice formation, this icing machine is operated cyclically with an ice-formation and a thaw cycle. In contrast, ice formation is not desirable in a solvent condenser for a solvent recovery apparatus in which the solvent to be recovered expediently flows through the condenser to avoid interrupting the continuous operation of the apparatus by removal of the frozen solvent.